- Presence of any MRI/tDCS/TMS risk factors: a) an electrically, magnetically or mechanically activated metal or nonmetal implant including cardiac pacemaker, intracerebral vascular clips or any other electrically sensitive support system; b) non-fixed metal in any part of the body, including a previous metallic injury to eye; c) pregnancy, since the effect of tDCS on the fetus is unknown; d) history of seizure disorder or post-stroke seizure; e) preexisting scalp lesion, bone defect or hemicraniectomy.